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Old 19th September 2003, 07:16 AM   #1
Hamish is offline Hamish  Australia
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Default Marantz preamp

Sorry if some of these questions sounds pretty basic, but this is my first attempt at anything involving tubes, so please bear with me.

i've been collecting/butchering old equipment for parts, and i'm just about to start on the Marantz 7 pre. First off, i've got a 6x4 rectifier, and i was wondering if this would be strong enough to supply both channels (models in PSU designer say that it gives up). Also, the transformer i have has a 6.3v tap for the heaters, and i was wondering if it was worth running these at DC, or just leaving them how they are.

Another thing, do i need to include the balance pot, and does the volume pot need to be so large (not so easy to get hold of).

And finally, i believe there are various mods/updates you can do to this circuit, but i can't seem to find any. I did read somewhere that there is an improvement if you run a B+ of 250v to all tubes.

Any help is most appreciated.

Thanks,
Hamish
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Old 19th September 2003, 08:12 AM   #2
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My impressions of the 7: phono is not bad at all, weakish bass but some magic in the mids; line is simply not worth building. I think i used 5U4G and regulated the heaters. Better designs are available today.
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Old 19th September 2003, 08:20 AM   #3
SHiFTY is offline SHiFTY  New Zealand
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According to the duncanamps.com database (well worth downloading btw) a 6x4 can handle 70mA at 325V. So I think it would be just cruising along in your application.

In my opinion, it is definitely worth running 12AX7 on DC heaters. Reduces noise and hum by quite a lot. A diode bridge followed by C-R-C filtering will do nicely, adjust the R to get 6.3 V exactly. Also ground one side of the filaments.

You can omit the balance pot if you like just use resistors.
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Old 19th September 2003, 08:25 AM   #4
Hamish is offline Hamish  Australia
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Thanks. I've been fiddling with the
PSU designer and i'm starting to come to grips with it.......

Is the line stage really that bad?
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Old 19th September 2003, 01:17 PM   #5
TJ is offline TJ
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Hi , ive a marantz 7 +9 reissu and the sound not that bad!! fast and dynamic !! solid soundstage !!if u like this type of sound ! the only thing is the phono stage ... not enough gain ! check ur cart . some cart not suitable for this phono amp . hope this help !
cheers
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Old 19th September 2003, 01:25 PM   #6
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Default Re: Marantz preamp

Quote:
Originally posted by Hamish
i'm just about to start on the Marantz 7 pre.
DONT!

It's a huge piece of crap, speaking from the experience of owning an original which was then modified all over the place (regs, caps, resistors, topology) before being restored and sold on to a collector.
Yuk! Yuk! Yuk!

The worst aspects of tubiness and poor resolution.

For your time and effort you can do much better. Use another design.

The only reason I'd like to own one today is so that I could sell it on again to another collector for an obscene amount of money.
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Old 20th September 2003, 12:01 AM   #7
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Hi,

Quote:
For your time and effort you can do much better. Use another design.
A tripple amen from me.

Cheers,
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Old 20th September 2003, 12:55 AM   #8
Hamish is offline Hamish  Australia
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Any suggestions then? i like this one because the 12ax7's are pretty easy to get and i have a few here anyway. I want a REALLY good phono stage (but not too complicated). That's my main aim.

fdegrove,

i found this on another thread, and you mention having done a phono stage similar. Could i get any more information on that, if possible? Obviously ye olde Marantz 7 is a reviled piece of equipment around here..........
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Old 20th September 2003, 01:09 AM   #9
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Hi,

Quote:
i found this on another thread, and you mention having done a phono stage similar.
Did I?

Hmmmm....I probably referred to the output stage I think.

The image you posted is nothing more than an anodefollower, RC coupled into another anode follower, direct coupled into a White cathode follower with NFB applied from output to input.

It may be some linestage but it certainly isn't a phono stage...

Cheers,
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Old 20th September 2003, 01:14 AM   #10
Hamish is offline Hamish  Australia
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Well, i'm aware it isn't a phono stage.........
but it shouldn't be too hard to work an active RIAA eq into the NFB (hopefully). So this should sound ok as line level pre? Sorry, but i have zero experience with tube topologies and sounds.

here's the thread: Comments on a preamp design
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